This invention relates generally to absorption heating and cooling systems and, in particular, to a refrigerant storage apparatus therefor.
As is well known, in an absorption heating and cooling system, a refrigerant is initially brought together with an absorbent capable of holding a high concentration of refrigerant to produce a solution suitable for use in the process. Under operating conditions that vary, the amount of refrigerant necessary to keep the system running efficiently will also vary. During operation in the cooling mode, the concentration of refrigerant is preferably relative below, i.e.; the solution is preferably relatively strong. Under this condition, the factors that limit the concentration of refrigerant are the need to prevent cavitation from occurring in the refrigerant pump of the evaporator or crystals of absorbent from forming in the sump of the absorber. As a result, it is common practice to equip the system with a cooling mode refrigerant adjusting system which includes a storage reservoir that is able to store enough refrigerant to prevent the solution from becoming too strong, and to store refrigerant in or release refrigerant from this reservoir as necessary to keep the concentration of the solution within acceptable limits as the demand for cooling fluctuates over the range of conditions over which the system is designed to operate. The storage reservoir often takes the form of the sump located within the system condenser. Since the range of refrigerant concentrations necessary to accommodate this range of conditions is relatively small, the storage capacity which this sump must have in order to accommodate this range of conditions is also relatively small.
One example of a cooling mode refrigerant adjusting system of the above described type is described in unexamined Japanese application 62-178 858, which is assigned to Ebara Ltd. of Tokyo, Japan. In the latter application, there""s disclosed an absorption machine in which the gravity flow of liquid refrigerant between the system condenser and the system evaporator is controlled in response to certain sensed system related conditions, such as the solution temperature as it is leaving the absorber. The reservoir for liquid refrigerant is provided inside the condenser and refrigerant is supplied to the evaporator through a first flow path under normal operating conditions. Upon a sensing of an operational condition that demands an increase in the quantity of refrigerant, a second flow path is opened which supplies additional refrigerant from the condenser sump to the evaporator.
Another example of a refrigerant adjusting system is described in U.S. Pat. No. 6,067,807, which is commonly assigned herewith, and which is hereby expressly incorporated herein by reference. In the latter patent, there""s disclosed an absorption type machine in which refrigerant is stored in a holding tank that is separate from the condenser sump and that is filled via a refrigerant bleed line. The desired refrigerant concentration is then maintained by releasing refrigerant from the holding tank under the control of a microprocessor in response to the sensing of a need for additional refrigerant.
An example of a refrigerant adjusting system that is specially adapted for use in an absorption type refrigerator is described in U.S. Pat. No. 5,806,325 (Furukawa, et al.). In the latter patent there""s described an absorption type refrigerator in which a storage reservoir is formed in the condenser by a dam with an array of holes that allows the rate at which refrigerant is released to vary as a function of the rate at which refrigerant condenses and, consequently, as a function of the cooling load that the refrigerator must support.
In addition to the need for refrigerant storage to accommodate load fluctuations during the cooling mode as described above, there is also a need to store refrigerant during operation in the cooling mode, and to release that refrigerant to the system during operation in the heating mode. That is, during operation in the heating mode, the solution is preferably as weak as the capacity of the system permits. Accordingly, when an absorption heating and cooling system is switched from operation in its cooling mode to operation in its heating mode, it is desirable to introduce as much additional refrigerant into the system as is possible. In accordance with the prior art, the additional refrigerant necessary to enable the system to operate efficiently in its heating mode has been provided in either of three ways.
One approach is to provide an evaporator sump which is sufficiently large to store the refrigerant that is not being used while operating in the cooling mode. The problem with this is that the evaporator must be unnecessarily large to accommodate this larger sump thereby adding expense and significantly increasing the footprint of the system
Another approach is to locate a storage tank in the condenser vessel. Although this is preferable over storing refrigerant in the evaporator, it is still undesirable because of the need to have a larger condenser vessel than would otherwise be necessary. An example of this approach is shown in copending U.S. patent application""s Ser. No. 09/491, 667, filed Jan. 27, 2000, which is commonly assigned herewith, and is hereby expressly incorporated herein by reference. In this application, there is disclosed an absorption machine in which refrigerant is stored in the reservoir located in the condenser during cooling mode operation and then emptied by a valve into the evaporator sump when changing over to the heating mode operation. It is also mentioned that the reservoir may be located outside of the condenser, but in any case, it is positioned so as to fill from the condenser by gravity. That is, in order to avoid the use of a pump, it must necessarily be located vertically below the condenser. This requirement presents a significant restriction on the design possibilities and severely limits the designer from storing refrigerant in locations that may be more convenient, practical and economical.
In view of the foregoing, it will be seen that, prior to the present invention, there existed a need for a simple, inexpensive, and practical approach in an absorption type heating and cooling system for storing refrigerant in a convenient location during operation in the cooling mode for release to the evaporator sump when switching over to operation in the heating mode.
In accordance with one aspect of invention, there is provided an absorption type heating and cooling system with a refrigerant storage tank having a capacity which permits the storage of sufficient refrigerant which, when released to the system for operation in the cooling mode, will result in an efficient cooling operation, which storage tank may be physically located in a position that is vertically above the condenser so as to give the designer greater flexibility in spatially arranging the various components within the system.
In accordance with another aspect to the invention, of the absorption system is a double effect machine having both high-temperature and low temperature generators. The high-temperature generator is fluidically coupled to the storage tank in such a way that refrigerant vapor passes from the high-temperature generator and through the low temperature generator, where it gives up its heat and is converted to liquid form, with the liquid refrigerant then passing on to the refrigerant storage tank. The pressure difference between the high-temperature generator and the refrigerant storage tank is sufficient to cause the liquid refrigerant to flow into the storage tank even though the storage tank is located at a relatively high elevational position.
By another aspect of the invention, the storage tank has an overflow structure which provides for the storage of a predetermined volume of refrigerant, with any further flow of refrigerant into the storage tank being caused to overflow into a conduit and pass by gravity to an evaporator sump. A valve is provided to fluidically interconnect the storage tank to the conduit, such that when the valve is opened, the stored refrigerant is drained from the tank and flows through the conduit to the evaporator sump.
By yet another aspect of the invention, the condenser is fluidically interconnected to the conduit passing to the evaporator sump, such that the condensate forming in the condenser passes by gravity flow to the evaporator sump during cooling mode operation.
In the drawings as hereinafter described, a preferred embodiments is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention.